A mass air flow sensor assembly is designed to sense, and control, the air to fuel mixture ratio in a gasoline, internal combustion engine. The sensor assembly operates by measuring the temperature differential between air and gasoline molecules. By doing this it can determine what the mixture ratio of these molecules is, and cause signals to be sent back to a mixture control. A desirable mixture is then achieved by automatic adjustment of the mixture control.
The temperature differential between molecules is actually determined by a nickel foil serpentine sensing circuit. The sensing circuit is laminated between two thin sheets of plastic film. The film in this sensing circuit laminate may be purchased as a unit from companies like Sierra, of California, which identifies it as a "Kapton".
The assignee of the present invention, Capsonic Group, Inc., has manufactured mass air flow sensor assemblies for several years. Initially the process involved supporting a Kapton and a terminal strip stamping from one side in an injection mold die and partially encapsulating the two elements in a plastic dielectric from the other side. A second molding operation then encapsulated the Kapton and stamping further, from the other side, welding it to the first molded panel.
This sensor assembly construction was a marked improvement over assemblies which had previously been made. In conventional constructions at that time, two molded blocks of plastic were glued together by hand, with a Kapton in between. The circuitry was entirely separate. This was a labor-intensive process and, by the very nature of this process, had quality control problems.
The method developed by Capsonic Group, Inc. eliminated much of the hand labor but subjected the Kapton to substantial stress during the fabrication operation. As a result, the Kapton sometimes suffered indiscernible temperature and pressure damage, resulting in subsequent delamination of the Kapton during operation of the sensing assembly.